U.S. Pat. No. 3,653,689 of Sapy et al. discloses a releasable coupling for a fluid-carrying tube; the entire disclosure of this patent is hereby incorporated by reference into this specification. The coupling of this patent contains means defining first, second, third, and fourth stepped concentric bores, a collar retained in the first bore and having an inner surface inclined to the axis of said bore, and a clamping member mounted within the collar for axial movement relative thereto and having a bore slightly larger than the diameter of the tube. The clamping member contains a plurality of flexible jaws and means o said jaws cooperating with the inclined surface to drive the jaws inwardly upon relative movement between the collar and the jaws to clamp the tube. The coupling also contains a packing ring retained in the second bore to provide a seal between the outer surface of the tube and the wall of the second bore, the third and fourth bores serving to locate the tube.
The coupling of the Sapy patent has found widespread commercial acceptance, especially for the use of connecting semi-rigid plastic tubing to automatic air-control components. However, the prior art discloses that this coupling, and others like it, are not also suitable for liquid applications.
By way of illustration, U.S. Pat. No. 4,304,426 of Robert A. Francis discloses, at lines 19-31 of column 1, that "Australian Patent specification No. 455,164 in the name of S. A. Legris Fils describes a pipe fitting in which a collet or thimble is interposed between the pipe and the body of the fitting. The collet is designed to grip the pipe to prevent it being withdrawn from the fitting and a `O` ring seal provided in front of the collet seals the connection. Whilst fittings of this type can cater for different pipe diameters using different `O` rings and collet sizes, testing has shown that such fittings, whilst they may be suitable for small bore high pressure air applications, do not perform satisfactorily when used for liquid applications."
It is an object of this invention to provide a releasable coupling for an air-carrying tube that will also perform satisfactorily when used for liquid applications.
It is another object of this invention to provide a releasable coupling for an air-carrying tube which will have a substantially longer service life than the prior art releasable couplings.
It is yet another object of this invention to provide a releasable coupling for an air-carrying tube which, for any given pressure, has a substantially lower leak rate at high temperatures than the prior art releasable couplings.
It is yet another object of this invention to provide a releasable coupling for an air-carrying tube which, for any given pressure, has a substantially lower leak rate at low temperatures than the prior art releasable couplings.
It is yet another object of this invention to provide a releasable coupling for an air-carrying tube which will require substantially less force to connect and disconnect than prior art releasable couplings.
It is yet another object of this invention to provide a releasable coupling which, after extended use, will require substantially less force to connect and disconnect than prior art releasable couplings.
It is yet another object of this invention to provide a releasable coupling for an air-carrying tube which has substantially greater long-term reliability than prior art releasable couplings.
It is another object of this invention to provide a process for producing a releasable coupling for an air-carrying tube that will also perform satisfactorily when used for liquid applications.
It is another object of this invention to provide a cartridge assembly which may be press-fit into a body containing a multiplicity of stepped bores to produce a releasable coupling for an air-carrying tube that will also perform satisfactorily when used for liquid applications.
It is another object of this invention to provide a cartridge assembly which may be screwed into a body containing a multiplicity of stepped bores to produce a releasable coupling for an air-carrying tube that will also perform satisfactorily when used for liquid applications.